The present invention relates generally to current sensing devices for electrical systems, and more particularly to timed reset fault indicators for alternating current power systems.
Various types of self-powered fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems and derive their operating power from inductive coupling to the monitored conductor, and test point type fault indicators, which are mounted over test points on cables or associated connectors of the systems and derive their operating power from capacitive coupling to the monitored conductor. Such fault indicators may be either of the manually resetting type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E.O. Schweitzer Manufacturing Company of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477, 4,063,171, 4,234,847, 4,375,617, 4,438,403, 4,456,873, 4,458,198, 4,495,489, 4,974,329, 5,677,678, 6,016,105, 6,133,723 and 6,133,724.
Detection of fault currents in a monitored conductor by a fault indicator is typically accomplished by magnetic switch means, such as a magnetic reed switch, in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the magnetic switch actuates a trip circuit that produces current flow in a trip winding to position an indicator flag visible from the exterior of the indicator to a trip or fault indicating position. Upon restoration of current in the conductor, a reset circuit is actuated to produce current flow in a reset winding to reposition the target indicator to a reset or non-fault indicating position.
Some prior art fault indicators utilize light emitting diodes (LEDs) to display a fault condition. However, LEDs require a source of power, such as an internal battery. Even if the LEDs are controlled to flash intermittently, the intermittent current drain from the internal battery is not insubstantial, and periodic replacement of the battery is required.
In certain other applications, the need arises for a fault indicator which will continue to display a prior fault condition for a predetermined amount of time, such as in the range of one hour to twenty-four hours, rather than self-resetting upon restoration of current in the conductor. The fault indicator should be capable of self-resetting after termination of the predetermined time.
Some of these applications also require voltage in-rush restraint and/or current in-rush restraint to prevent false tripping due to voltage and/or current surges, such as when a reclosing relay of a power distribution system closes.
In certain of these applications, the need also arises for auxiliary contacts in the fault indicator for indicating or recording the detection of a fault current at a location remote from the fault indicator. For example, where fault indicators are installed in each of multiple distribution circuits fed from a common source, it may be desirable to monitor the fault indicators at a central monitoring facility to enable a fault to be quickly isolated. Repair crews can then be efficiently dispatched to the known location of the fault.
Because of the compact construction and limited power available in self-powered fault indicators, it is preferable that the desired functions of the fault indicator be accomplished with minimal structure and with internal circuitry that has minimal current drain on a high capacity battery. The fault indicator must also provide highly reliable and extended operation over a number of years.
Because fault indicators only trip when some high current level, such as 600 or 800 amperes, is exceeded, there is a need for a fault indicator that can forewarn of overload conditions, such as greater than 500 to 600 amperes, on a monitored conductor. Of course, such overload conditions could cause the fault indicator to indicate a fault on the conductor if the overload increases to the trip point of the fault indicator, when in fact, no fault condition exists.
There is a further need for such an overload indicating fault indicator that operates from energy coupling to the monitored conductor, i.e., operates without the need for a battery.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator for detecting and indicating an overload indication.
Another object of the present invention is to provide a fault indicator with an overload indicator that provides a first indication for a predetermined time after an overload threshold has been exceeded.
A further object of the present invention is to provide a fault indicator with an overload indicator that provides a second indication for a predetermined time after the current load on the monitored conductor fall below the overload threshold.
Yet another object of the present invention is to provide such a fault indicator with in-rush restraint to avoid false tripping on line surges.
A further object of the present invention is to provide such a fault indicator with auxiliary contacts to provide contact closure indicative of fault occurrence and overload occurrence.
This invention is directed to a fault indicator for indicating the occurrence of a fault current in an electrical conductor. The fault indicator has a housing, an indicator flag or a light emitting diode (LED) that becomes visible from the exterior of the fault indicator upon the occurrence of a fault and which may be reset to a non-fault indicating condition after the occurrence of the fault, and electronic circuitry for sensing a fault, for actuating the indicator flag or LED to a fault indicating position and for resetting the indicator flag or LED to a non-fault indicating position a predetermined time after the fault has occurred. An overload indicator provides an overload indication, such as a fast flash rate, when an overload threshold is exceeded, and provides a different overload indication, such as a slow flash rate, when the line current in the monitored conductor falls below the threshold. The electronic circuitry may also include voltage in-rush restraint and/or current in-rush restraint to avoid false tripping of the fault indicator during voltage and/or current surges. Auxiliary contacts also provide an indication of This invention is directed to a fault indicator for indicating the occurrence of a fault current in an electrical conductor. The fault indicator has a housing, an indicator flag or a light emitting diode (LED) that becomes visible from the exterior of the fault indicator upon the occurrence of a fault and which may be reset to a non-fault indicating condition after the occurrence of the fault, and electronic circuitry for sensing a fault, for actuating the indicator flag or LED to a fault indicating position and for resetting the indicator flag or LED to a non-fault indicating position a predetermined time after the fault has occurred. An overload indicator provides an overload indication, such as a fast flash rate, when an overload threshold is exceeded, and provides a different overload indication, such as a slow flash rate, when the line current in the monitored conductor falls below the threshold. The electronic circuitry may also include voltage in-rush restraint and/or current in-rush restraint to avoid false tripping of the fault indicator during voltage and/or current surges. Auxiliary contacts also provide an indication of any fault, such as to a remote location.